Safety connection for snduction-goll systems



(No Model.) I 2 Sheets-Sheet 1. E. THOMSON.

SAFETY CONNECTION FOR INDUCTION 0 No. 496,918.

OIL SYSTEMS. Patented May 9, 1893.

fm/enior ZZM/w T/mmsom, a, A; 92am inessesz- (No Model.)

E 2 Sheets-Sh t SAFETY CONNECTION FOR INDUCTION COIL SYSTEMS. No. 496,918.

Patented May 9, 1893.

gvwemtoz UNITED STATES PATENT @FFEQRQ EL'IHU THOMSON, or LYNN, MASSACHUSETTS, ASSIGNOR nousron ELECTRIC COMPANY, or CONNECTICUT.

TO THE THOMSON- SAFETY CONNECTiON FOR moucrson coitsrsrewzs.

SPECIFICATION forming part of Letters Patent No. $96,918, dated May 9, 1893. Application filed OotoberB, 1888- Serial in. 287,564. (No model.)

To all? whom itmay concern,-

Belt known that 'I,ELIHU THOMSON, a citizen of the United States, and a resident of Lynn, in the county of Essex and State of Massachusetts, have invented a certain new and useful Safety Connection for Induction-Coil Systems, of which the following is a specification.

In the operation of electric circuitscarry- 1'0 ing currents of high tensiou,a source of dauger arises from the fact that aneighboring local circuit or conductor, or conducting material, may become accidentally connected with the high tension circuit. Under this cour5 dition a person'whose body forms a ground connection from the local circuitor conductor may receive a dangerous shock if at the same time there be a distant ground upon the main or high tension circuit. This danger is pres-' cut in greater or less degree whether the neighboring conductor be carrying an electric current or not, and it is the object of my invention to provide for any condition where from the location or nature of the neighbor- 2 5 ing conductor it may acquire accidentally, for the time being, the tension of a-high tension circuit and so may become a source of dauger to a person touching the same.

My invention while applicable to many cases is especially designed for application to systems of electric distribution in which the local or neighboring circuit is the path of currents derived, abstracted, or converted from the main but=of lower tension, a well known example of such system being the al-v ternating current system of distribution by induction coils or converters. Other systems are referred to in my prior patent No. 322,138.

In my present invention I aim, as in my 40 prior patents, to protect a person touching a conducting medium, for the time being, in connection with the high tension circuit, by means of a low resistance ground or circuit from such conducting medium around his body, but my present invention differs from mypriorinvention in that in the former case there isalways a low resistance safety ground Wlreor circuit from the local or secondary circuit or from the septum between the -pri-. 5o mary and secondary coils of the converter,

while in the present instance the low-resistas film and vacuum cutouts arealso used for the same purpose, the' only difference being ance ground circuit is not established until after the high potential of the primary or main is transmitted to the secondaryor other conductor in proximity to such main.

My invention therefore furnishes all the protection afforded by the employment of the device forming the subject of my prior patent without, however, any of the objections which are incident to the use of a permanent low resistance ground connection from the secondary or local circuit or other conducting medium which is normally disconnected from the main line carrying the current of high tension but which, it permanently connected to'earth by a low resistance, might inyite the escape of the high tension currents from the main line.

My invention consists essentially in the combination of a main line circuit carrying currents of comparatively high potential, a local or separate circuit or conductor which is normally disconnected from said line but is liable to receive the high tension current escaping from the line to said separate conductor or circuit, and aground circuit orconnection taken from a part of the apparatus or circuits normally disconnected from the main line but containing a high resistance and means for e'stablishinga substitute low resistance safety ground connection by the action of any high potential current -which may escape from the line to the parts disconnected therefrom and pass over the high resistance to ground.

ln'carrying out my invention It may use as the means for establishing the substitutelow" resistance circuit, any devices known in the electric art whereby a current flowing on a circuit may establish another circuit or con nection made up in whole or in part-of the wires or circuit through which said current flows or consistiugot wires or paths entirely independent or separate from the wires'or paths which, carry the initial current; Various devices are known to electricians for this purpose, the simplest-being an electro magnet the armature of'which shall close electric contacts whensthemagnet is excited to a sufiicient degree. Other devices vknown that in the case of a film'cut out the path or circuit established by the action of the initial current is principally made up of the-same wires orconductors through which the current first flows.

Other devices than those specifically described herein are known to electricians and will not be set forth in detail those described being sufiicient to illustrate the principle of my invention which consists, as before stated, in the combination with the local or independent conductor normally disconnected from the main line carrying j the current of high tension, of a high resistance ground current, thus giving rise to movement of con-' tacts for establishing proper relationsor conditions ofan electric conductor or conductors suitable for forming an electric circuit or con-' nection. Some of vthe expedients that may be employed will be presently described. The high resistance may be composed of any medium and may even consist of a rarefied gas or vapor, as will be described.

' My invention consists furtherjn certain dc tails which will be described and then specifically claimed.-

Inthe accompanying drawings :-Fignres 1, 2, 3,4, 5 and 6, illustrate various modified arrangements of oneway of carrying out my in-. vention. Figs. 7, 8, 9, 10, 11 j and 12,. -show modifications in' the manner of practicing my invention as will be more particularly'stated in the detail description of these figures.

In the form of my invention illustrated in Figs.- 1' to 6, the normal ground circuit is made of high resistance by the interposition of a thin'layer or film of an insulating medium between two electrodes in the circuit. The'high potential current punctures or pierces the film and by so doing establishes a'direct conncotion between the electrodes thus forming the low resistance or safet'ycircuit. Thus in Fig. 1, a and b, indicate a high potential primary line, a-brauch .fromywhichlpasses through a primary coil P, in the ordinary way,- wound for high potential, andwhich: is the primaryof an induction coil. The secondary S, of the same coil, wound parallel to the coil P, is used to feed a consumption circuit of lights L,L, or other devices in the usual manner, suitable -fuses being-provided in both primary and secondary circuits f, f, f, f. From some "point. in the secondary circuit, preferably "near the middle, 3, connection is takento acontact piece K, bearing on a film or a thin layer of insulating material F, of oiled paper or of other material, and with an earth plate.

or connection G, on the other side of the film, forming, as it were a film cutout or weak spot in the insulation between the earth or ground and the secondary circuit. So long now, as no connection whatever exists between the primarycoil or circuit P, receiving high potential discharges and the secondarycoil or circuit S, in which low potential currents are induced there will be no discharge tending to puncture the film F. it, however,

a connection, either temporary or permanent,

is formed between the circuit a, b, or primary coil P, and the secondary coil S, or other conductor such that the potential of the primary line or other conductor is taken up by the secondary, the film F,is punctured by the en deavcr of the high potential current to leak to ground, provided, of course, thatanywhere von the primary circuit a, b, a sufficient leakage or static ind uction al capacity or tendency exists to give rise to the necessary discharge to earth in puncturing the film. It is need-- less to say that such leak orstaticinductional capacity is-usually found in'a circuit of considerable length. When the film F, has been punctured, the conductor or secondary coil S,

is then, connected solidly to earth by a cir-. cult of low. resistance and no danger can er:-

ist in touching the wires of the secondary circuit, even though connected with the primary circuit, when a person may be at the same time grounded, for he is already shunted by the connection through the electrodes K, G, to earth. After the film is punctured the de:

vice becomes the same in essence as that described in my former patent.

, In. my present. invention the low resistance grounding of the secondaryor other conductor to earth does, not occur until the secondary has reached the same potential ora large part of the potential of the primary, when an instantaneous puncturing of. the film F, takes place.

It'may be well'in some cases to shunt the film as it were, or'rather toplace around the film a, condenser, as in Fig. 2, of small ca-- pacity, the condenser being represented at C,

and consisting of platesseparated by insulating material in the ordinary way, the plates with the connection to the coil S, or septum near it. 'In this case a small amount ofstatic induction 'or. leakage may occur between the primary and secondary without forcing the puncturing of the film F, and the formation of a good connection bet'weenthe metal'pieces normally separated loy said film, the condenser-0, acting to prevent the ground which would reach the secondary by such small or slight induction or leakage; but if a solid conopposed to each other being respectively connected one to the ground circuit and the other nection between the'pritnary coil Rand the a secondary coilS, be. formed, then the con denser 0, is insuificient' in. capacity toco nk dense or lower the potential-of -,'thealterna'ting discharges which reachthe secondary and the film is at once punctured,making the with the wiresm, n',

connection to earth as before and shunting the condenser.

In Fig. 1, the connection has been shown as made to the secondary itself, but the line fed by it may also be .in connection. Thus in Fig. 3, the dotted line from the secondary represents aconnect'ion similar to that otFig. 1, but in place thereof, or in addition thereto there may be arranged connections m, n, one wire from each side of the local circuit, which wires m, n, terminating iii-spring contact pieces K, K, bearing on films F, F, orthin layers of insulating material, bear down on stationary blocks G, G, which blocks are connected to the earth plate E. The condenser G, isin this case a double one,one "pole or plate ofi which is connected to the'earth plate and the other plates respectively connected or the: pieces K, K, as shown." In some cases this condenser might be dispensed with and the connections thereto 7 removed leaving the double film arrangement intact. The breaking through of either one of these films F, F will ground the secondary, and the breaking through-ct both simultaneously would not only ground thesecond ,ary but extinguish the lights. L, L, by causinga short circuit of the secondary which would melt thefuses fif,"in the secondary circuit, thus disconnecting the secondary-or] local wire from the line feedingthe'lights- It is useful to combine the two fi l-m switches or connectors into a si'nglecompact device, such as is represented in Fig. 4:. .Here' the earth connection is made to a spring strip or strips of metal G, G, whose ends bear upon the films F, F, placed on buttons ,K, K, as

shown, the buttons K, K, being placed on a common base and connected asin Fig. 3, with the sides of the working-circuit or with any other part of the secondary circuit. There is a tendency on account'of the spring of the pieces G, G, bearing upon the films to the formation of a connection between the opp0s- I ducting septmninterposed ing contact pieces should the films be punct ured. The whole of the parts can be mounted upon asuit-able insulating base. This device may be attached to any circuit in existence in whicha high potential current is converted by induction or otherwise into a low potential current on a local and separate circuit and forms an elfi'cient safe-guard. when the films F, F, are not of. too great thickness or too diflicult to puncture.

ground wire or circuit as leadingfrom a conbetween the primary or main and the secondary or local circuit and which septum assumes or partakes of the dangerous potential of the-secondary or local whcnever'the latter becomes connected with the main or principal circuit; carrying the current of high tension by any discharge tending to pass from the high potential primary .to the'secondary. This sheath or septum is placed between the primary and In my former patent I have shown the safety the secondary coils wherever they are opposed,

- narily necessary, cult should include some device suchas an or wherever they are capable of having a connection formed between them, either directly or through the iron core itself of the induction coil, drc. Thus I wrap either the primary-or the secondary coil with a ribbon of thin copper, connecting the ribbon either togroundas in my former invention or conmeeting it with the film switch F, as in Fig. 5, I, representing the interposed conductor between the prima 'y coil P, and the secondary coil S, and T, the earth plate. Y

The interposed sheath may, as in Fig.6, be formed by wrapping a copper sheet over the secondary coil S, so as to either cover it in part or entirely, but so that no closed circuits may be set up in the copper sheet itself. This interposed sheath is applicable to any form of induction coil, all that is necessary beingv to so dispose the sheath that it shall inclose so much of either the primary or secondary or both as may be subjectto the possibility of interchange of current or electric action between them.

In Fig.7, I have shown how the high tension current when it forces itself over the high resistance ground circuit may establish its low resistance circuit by means of a magnet. The low resistance circuit is throngh'the contacts of a spring or otherwise actuated switch S that is normally held open by the armature of amagnet H, in the high resistance circuit formed as before; When at the first passage of the high tension current the magnet is energized its armature is attracted and the low resistance or safety circuit established through S inobvious manner.

It is obvious that, as shown in Fig. 9, the 1 electrodesK and G, and interposed film might be omitted and the high resistance obtained in other ways as by winding the magnet-with ver fine wire or by interposing in the circuit an artificial resistance of other character in addition to the resistance of the magnet.

By a well known device indicated in Fig.

10, the switch of the low resistance circuit may be held closed by the current of such circuit instead of by a released spring as in Fig. 7. This is effected by providing the mag met H, with a 'coil circuit as indicated. When the low resistance circuit is established otherwise than by the disruptive action of the high tension upona material normally holding electrodes apart, as in Figs. 1-5, the high resistance path may be formed through electrodes separated by H in the low resistance aninsulatinginediuin, such as rarefied air or 1 gas. In this case it is desirable, and ordh that the high 'resistancecirelectro magnet by acting npon which the'initial discharge to earth may operate or bring about the operation of electrodes or contacts which shall close the low resistance circuit.

Such a form of my invention'is indicated .in. Fig. 8, where the electrodes K, 'G, are shown held in close proximity in a globe or ceiver M, of glass or other material partia y exby means of the switch or contact lever Fig. 11, illustrates one of the waysin which the heating eifect of the current of high tension' upon the high resistance circuit may be employed to bring about the establishment of the low resistance path. The high resistance ath consists of a heatin coil a connectedv p O 3 to earth and wound around a bar of 'iron,copper, or other conducting material to which the heat produced by the high tension current in the coilmay be" imparted. Thecopper bar forms a part of the low resistance path being attached to the normal high resistance circuit at the point 7, as indicated, and having at its end a fusible ordestructible film of shellac or pyroxyline, or other suitable material which normally holds a contact device b out of electrical connection with the bar. The contact 11*, is connected directly to ear th, and when the film is destroyed or removed, owing to the large heatingeflects produced by the high tension current, the con-.

tact b establishes connection with the end of the copperbar thus establishing the low resistance circuit in obvious manner. I

- In Fig. 12,- the normal high resistance path is shown as including a fine wire coil a ,'of an induction coil or transformer T. The secondary c of said transformer is of coarse wire and includes in its circuit a fusible strip d that serves to hold the low resistance circuit closer S open. The cnrrent'normally leaking to earth through the 'coil a is not suificient to produce fusion of the (strip d but, when through connection of the local circuit or coil with the high tension circuit, a

. rim or connections from a conductor appacurrent of large volume forces its wayover the normal high resistance so that the heating current is increased in the secondary 0 the device or stop (1 melts. and permits the switch S, to close the low resistance path. It is of course understood that the arrange ment shown in Fig. 12, is especially designed for use with systems using alternating or varying high 'tensioncurrents upon the main. The special devices shown in Fig. 12, forms the subject of another application for Patent filed by me. (D. 489.)

Other means will readily occur to electricians whereby the current in ahigh resistance circuit may bring about the establishment of a circuitof low resistance formed in greater or less degree of the original path'or,

entirely independent thereof. .1 wish it to be understoodthat. my invention is not limited to any special devices but. consists in the application of snchdevices in a ground con nee ratus or conducting object normally separated from b'ut'liable to accidental connectionwith' a circuit carrying current of high tension, the purpose being to provide for the establish ment of a low resistance ground connection as ameasure of safety when dangerous or other abnormal condition arises, but at all other times to leave such circuit conductor, septum, or object in its normal or practically ungronnded electrical condition.

The use of the two electrodes connected in the safety ground circuit but normally insulated from one another by athin film or layer of some insulating material and the applicatron to such device of a condenser in a shunt around the electrodes as hereinbefore described, I do not claim specifically in this application as these devices form the subject of said line but liable to accidental connection therewith, a ground circuit or connection taken from a part of the apparatus or circuits normally disconnected from the main line and of suificient high resistance not to interfere with ,the normal operation of such circuit, and means'for establishing a substitute low resistance ground connection by the action of high tension current accidentally escaping from the .line to the parts normally disconnected therefrom-and passing over the high resistance to ground.

2. The combination, substantially as described,ot a main line, a local or independent circuit or conductor normally out of connection with said main line, connectionsto earth from a part of the apparatus disconnected tension current accidentally escaping from the line but having an interposed high resisttension local line, an interposed converting from the line and adapted to receive any-high appliance, a ground connection from the local circuit or conductors containing an interposed high; resistance,'-and meansjor; establishing a substitute low resistance safety connection by normally supplied high tension current ofsaid mainline escaping therefrom to the local circuit and thence to ground through the high resistance. l 4. The. combination, substantially as described, of a high tension main line, a converter, a low tension local, a normal ground connection from the latter of considerable resistance, and means in the ground wire or connection for establishing a substitute low resistance safety'path or connection by the action of the normal high tension main line current accidentally escaping therefrom to the local and thence over said ground connection. T

5. The combination with a main line, of a local or independent lin'e, an interposed converter, a high resistance ground connection from each side of Y the local line adapted to form a path for the high tension current flowing from the main line, and an fuse between the converter and the local circuit whereby,

in case of the establishment of both grounds and consequent short circuiting of the local sideof the converter, the fuse may operate todisconnect the local wire or circuit from said converter. v

6; The combination, substantially as described, of a main line carrying alternating cnrrentsQa transformer, a local circuit sup- 2o plied with currents of lower potential from the secondarypf said transformer, aground be established.

Signed at Lynn, in the county of Essex and State of Massachusetts, this 26th day of September, A. D. 1888..

ELIHU THOMSON.

in case both low resistance grounds should 3o Witnesses:

J W. GIBBONEY, GEO. E. EMMONS. 

